Method for producing bis(trifluoromethyl)imido salts

ABSTRACT

The present invention relates to a novel process for the preparation of bis(trifluoromethyl)imido salts of the general formula (I):
 
[M a+ ] − [N(CF 3 ) 2 ] a   (I).

The present invention relates to novel processes for the preparation ofbis(trifluoromethyl)imido salts of the general formula (I):M^(a+)[(N(CF₃)₂)⁻]_(a)  (I)

The chemistry of the bis(trifluoromethyl)imido anion is generally basedon the chemical reaction of perfluoro(2-azapropene), CF₃N═CF₂, asstarting material (H. G. Ang and Y. C. Syn, Advances in InorganicChemistry and Radiochemistry, Vol. 16 (1974), pp. 1-64; A. Haas, GmelinHandbook of Inorganic Chemistry, 8^(th) Edition, Springer Verlag:Berlin, Heidelberg, New York (1991), Part 9, pp. 125-153; A. Haas,Gmelin Handbook of Inorganic Chemistry, 8^(th) Edition, Springer Verlag:Berlin, Heidelberg, New York (1991), Suppl. Vol. 6, pp. 196-214). Thiscompound can be prepared by fluorination of CCl₃N═CCl₂ using NaF insulfolane at 105° C. in a yield of 78% (E. Klauke, H. Holtschmidt, K.Findeisen, Farbenfabriken Bayer AG, DE-A1-2101107 (1971/1972)) or byphotolysis of CF₃N—(CF₂CFCl₂)Cl (G. Sawar, R. L. Kirchmeier and J. M.Shreeve, Inorg. Chem. 28 (1989, pp. 2187-2189)) in gas at roomtemperature (boiling point −33° C.), with special industrial apparatusesbeing necessary for the said compound.

Di[bis(trifluoromethyl)imido]mercury, Hg[N(CF₃)₂]₂, which is veryreactive, was synthesised for the first time by Young and his co-workers(J. A. Young, S. N. Tsoukalas and R. D. Dresdner, J. Am. Chem. Soc. 80(1958), pp. 3604-3606). This compound is a good reagent for theintroduction of N(CF₃)₂ groups into organic molecules (H. G. Ang and Y.C. Syn, see above; A. Haas, Gmelin Handbook of Inorganic Chemistry,8^(th) edition, Springer Verlag: Berlin, Heidelberg, New York (1981),Part 9, pp. 45-46), but is not a very stable compound since it isextremely sensitive to moisture. The synthesis of Hg[N(CF₃)₂]₂ isdifficult, time-consuming and requires special industrial apparatusesand expensive starting materials.

Caesium bis(trifluoromethyl)imide, [Cs]⁺[N(CF₃)₂]⁻, is a further optionfor the synthesis of bis(trifluoromethyl)amino compounds. This salt isprepared by simply passing perfluoro(2-azapropene) into a solution ofcaesium fluoride in dry acetonitrile (A. F. Gontar, E. G. Bykovskaja andI. L. Knunyants, IZV. Akad. Nauk SSSR, Otd. Khim, Nauk (1975), pp.2279-2282).

The disadvantage of this method consists in the formation of a dimericproduct through the reaction of the starting materialperfluoro(2-azapropene) with the caesium salt that has already formed.This reaction is unavoidable and results in the formation of complexproduct mixtures.

However, N(CF₃)₂ anions are readily accessible through the reaction ofsome metal fluorides withN,N-bis(trifluoromethyl)perfluoroalkanesulfonamides or -acylamides[“N(CF₃)₂ anion preparation, and its use”, EP 99 101 982]. This processenables the generation of Na, K, Rb, Cs, Ag, Cu(II) and Hg(II) saltswith N(CF₃)₂ anions. However, the analogous reaction ofN,N-bis(trifluoromethyl)perfluoroalkanesulfonamides or -acylamides withother metal fluorides (for example ZnF₂ and CdF₂) progresses only veryslowly due to the poor solubility of these fluorides in organicsolvents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical depiction of the electrochemical stability of anexemplary embodiment of the invention.

FIG. 2 is a graphical depiction of the conductivity of an exemplaryembodiment of the present invention.

FIG. 3 is a graphical depiction of the conductivity of a comparativeexample.

The object of the present invention was therefore to provide an improvedprocess for the preparation of bis(trifluoromethyl)imido salts.

The object according to the invention is achieved by a process for thepreparation of bis(trifluoromethyl)imido salts of the general formula(I)[M^(a+)][(N(CF₃)₂)⁻]_(a)  (I)in which

-   -   M^(a+) is a monovalent or divalent cation, and a=1 or 2,        characterised in that at least one trifluoromethanesulfonate of        the general formula (II)        [M^(a+)][(OSO₂CF₃)⁻]_(a)  (II)        in which    -   M^(a+) is a monovalent or divalent cation, and a=1 or 2,        is reacted with bis(trifluoromethyl)imidorubidium in solution,        and the resultant bis(trifluoromethyl)imido salt of the general        formula (I) is, if desired, purified and/or isolated by        conventional methods.

Preference is given to processes according to the invention in whichM^(a+) is a sodium, potassium, caesium, copper or silver cation, anda=1.

Particular preference is given to processes according to the inventionin which M^(a+) is a mercury, copper, zinc or cadmium cation, and a=2.

Particular preference is also given to processes according to theinvention in which a=1 and M^(a+) is a cation of the general formula(III)[([R_(b) ¹R_(c) ²R_(d) ³R_(e) ⁴]A_(x))_(y)Kt]⁺  (III)in which

-   -   Kt═N, P, As, Sb, S or Se,    -   A═N, P, P(O), O, S, S(O), SO₂, As, As(O), Sb or Sb(O),    -   R¹, R², R³ and R⁴ are identical or different and are    -   H, halogen, substituted and/or unsubstituted alkyl        C_(n)H_(2n+1), substituted and/or unsubstituted C₁₋₁₈-alkenyl        having one or more double bonds, substituted and/or        unsubstituted C₁₋₁₈-alkynyl having one or more triple bonds,        substituted and/or unsubstituted cycloalkyl C_(m)H_(2m−1),        monosubstituted, polysubstituted and/or unsubstituted phenyl,        substituted and/or unsubstituted heteroaryl;        where    -   n=1-18,    -   m=3-7,    -   x=0 or 1,    -   y=1-4, y=1 for x=0,        where    -   b, c, d and e are each=0 or 1, where b+c+d+e≠0,    -   A may be included in various positions in R¹, R², R³ and/or R⁴,    -   Kt may be included in a cyclic or heterocyclic ring,    -   the groups bonded to Kt may be identical or different.

The processes according to the invention also enable the preparation ofnovel bis(trifluoromethyl)imido salts which are difficult to access,such as, for example, cadmium, zinc or copper(I) N(CF₃)₂ salts. Novelsalts therefore represent a further subject-matter of the presentinvention.

The salts prepared in accordance with the invention can be used alone orin mixtures with other salts as conductive salts or additives inelectrolytes. Besides the salt or salt mixtures, the electrolytes alsocomprise solvents or solvent mixtures.

These electrolytes are employed in electrochemical cells (such as, forexample, primary and secondary batteries). They are preferably employedin capacitors and supercapacitors.

The starting materials bis(trifluoromethyl)imidorubidium and thetrifluoromethanesulfonate salts are both readily soluble in a number oforganic solvents. In addition, metal triflates are commerciallyavailable from a number of companies.

The reaction of Rb[N(CF₃)₂] and metal triflates at room temperature orbelow takes place rapidly, for example in accordance with the followinggeneral reaction scheme:xRb[N(CF₃)₂]+M(OSO₂CF₃)_(x)→M[N(CF₃)₂]_(x) +xRb(OSO₂CF₃)

In the process according to the invention, the conversion to abis(trifluoromethyl)imido salt of the general formula (I) is preferablycarried out at a temperature of from −60 to +60° C., particularlypreferably from −50 to +50° C., very particularly preferably at from −45to +30° C.

Preferred solvents for the conversion to a bis(trifluoromethyl)imidosalt of the general formula (I) are organic solvents, particularlypreferably polar organic solvents.

Very particularly preferred solvents for the conversion to abis(trifluoromethyl)imido salt of the general formula (I) are thesolvents acetonitrile, benzonitrile, dimethoxyethane and/orpropionitrile or a mixture of acetonitrile, benzonitrile,dimethoxyethane and/or propionitrile.

Preferred solvents according to the invention comprise ≦0.1% by weightof water, preferably ≦0.01% by weight of water, particularly preferably≦0.005% by weight of water.

In the preferred processes according to the invention, thetrifluoromethanesulfonate salt of the general formula (II) or thebis(trifluoromethyl)imidorubidium is employed in a molar excess of ≦3%or particularly preferably in equimolar amounts.

The rubidium triflate formed by the process according to the inventionhas limited solubility in organic solvents and can be separated off fromthe reaction mixture as a solid at low temperatures.

Preferred processes according to the invention are therefore those inwhich the bis(trifluoromethyl)imido salt of the general formula (I) ispurified by filtration at a temperature of from −90 to +30° C.,particularly preferably at from −70 to +20° C., after removal of thesolvent.

Further purification of a bis(trifluoromethyl)imido salt of the generalformula (I) is possible by extraction with dichloromethane and/or hexaneand/or diethyl ether. Extraction with dichloromethane is a preferredvariant of the present invention.

The invention is explained below with reference to examples. Theseexamples serve merely to explain the invention and do not restrict thegeneral inventive idea.

EXAMPLES Example 1 Synthesis of Bis(trifluoromethyl)imidosilver Salt

A solution of Rb[N(CF₃)₂] salt prepared from 0.083 g (0.79 mmol) ofrubidium fluoride and 0.227 g (0.79 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml ofdry acetonitrile was added to a solution, cooled to −20° C., of 0.205 g(0.79 mmol) of AgOSO₂CF₃ in 1.8 ml of dry acetonitrile with stirring.The mixture was stirred at −20° C. for one hour. A white sediment formedin the process. The solvent acetonitrile was removed by suctionfiltration at −20° C., and 4 ml of dry dichloromethane were added to theresidue. After the mixture had been stirred at −20° C. for ten minutes,the solution was separated from the residue, and the solvent was removedby suction filtration at −20° C. 0.149 g of Ag[N(CF₃)₂].CH₃CN wasobtained as a white crystalline substance, as demonstrated by analysis.The yield was 62.3%.

Analysis (amperometric titration):

-   -   Yield: 35.76% (Ag⁺);    -   Theoretical value for Ag[N(CF₃)₂].CH₃CN: 35.85% (Ag⁺);

¹⁹F NMR spectrum (solvent CD₂Cl₂, reference substance CCl₃F),

-   -   ppm: −44.56 s (CF₃)

¹H NMR spectrum (solvent CD₂Cl₂, reference substance TMS),

-   -   ppm: 2.08 s (CH₃CN)

¹⁰⁹Ag NMR spectrum (solvent CD₂Cl₂, reference point: chemical shift of1M AgNO₃

-   -   in D₂O set to 0),    -   ppm: 316.23 s, Ag

Example 2 Synthesis of Bis(trifluoromethyl)imidocopper(I) Salt

A solution of Rb[N(CF₃)₂] salt prepared from 0.080 g (0.766 mmol) ofrubidium fluoride and 0.218 g (0.766 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml ofdry acetonitrile was added at room temperature to a solution of 0.194 g(0.766 mmol) of CuOSO₂CF₃·CH₃CN in 1.8 ml of dry acetonitrile withstirring. The mixture was stirred for one hour. A white sediment formedin the process. The solvent acetonitrile was removed by suctionfiltration at room temperature, and 4 ml of dry dichloromethane wereadded to the residue. After the mixture had been stirred at roomtemperature for ten minutes, the solution was separated from theresidue, and the solvent was removed by suction filtration at roomtemperature. 0.150 g of Cu[N(CF₃)₂]·CH₃CN was obtained as a whitecrystalline substance, as demonstrated by analysis. The yield was 76.5%.

¹⁹F NMR spectrum (solvent CD₂Cl₂, reference substance CCl₃F),

-   -   ppm: −44.79 s (CF₃)

¹H-NMR spectrum (solvent CD₂Cl₂, reference substance TMS),

-   -   ppm: 2.03 s, CH₃CN

Example 3 Synthesis of Bis(trifluoromethyl)imidozinc Salt

A solution of Rb[N(CF₃)₂] salt prepared from 0.080 g (0.766 mmol) ofrubidium fluoride and 0.218 g (0.766 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml ofdry propionitrile was added at −45° C. to a solution of 0.155 g (0.383mmol) of Zn(OSO₂CF₃)₂·CH₃CN in 1.8 ml of dry propionitrile withstirring. The mixture was stirred for one hour at −45° C. A whitesediment formed in the process. The mixture was then cooled to −78° C.and left at this temperature without stirring for two hours. The solventwas removed by suction filtration, a small amount of CD₃CN (about 30%)was added, and the mixture was characterised by ¹⁹F NMR spectroscopy at−45° C.

The signal at −44.83 ppm is assigned to Zn[N(CF₃)₂]₂, which iscoordinated with the solvent.

In order to isolate the salt, the solvent was removed by suctionfiltration at −30° C., and the white solid which remained was, afterdissolution in dry CD₂Cl₂, employed for NMR spectroscopy. The NMRspectrum showed the presence of the propionitrile in the crystalstructure of the Zn[N(CF₃)₂]₂·C₂H₅CN salt. This salt has only lowstability as analysis substance at room temperature.

¹⁹F NMR spectrum at −40° C. (solvent CD₂Cl₂, reference substance CCl₃F),

-   -   ppm: −45.97 s (CF₃, the position of the signal is        concentration-dependent)

¹H NMR spectrum at −40° C. (solvent CD₂Cl₂, reference substance TMS),

-   -   ppm: 1.08 t (CH₃); 2.25 q (CH₂), C₂H₅CN

Example 4 Synthesis of Bis(trifluoromethyl)imidocadmium Salt

A solution of Rb[N(CF₃)₂] salt prepared from 0.080 g (0.766 mmol) ofrubidium fluoride and 0.218 g (0.766 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml ofdry propionitrile was added at −45° C. to a solution of 0.188 g (0.383mmol) of Cd(OSO₂CF₃)₂·2CH₃CN in 1.8 ml of dry propionitrile withstirring. The mixture was stirred for one hour at −45° C. A whitesediment formed in the process, the mixture was then cooled to −78° C.and left at this temperature without stirring for two hours. The solventwas removed by suction filtration, a small amount of CD₃CN (about 30% byvolume) was added, and the mixture was characterised by ¹⁹F NMRspectroscopy at −40° C. The signal at −42.53 ppm is assigned toCd[N(CF₃)₂]₂, which is coordinated with the solvent. At roomtemperature, the signal of the N(CF₃)₂ group in the ¹⁹F NMR spectrumshifts to −45.39 ppm. The Cd[N(CF₃)₂]₂·nC₂H₅CN salt has only lowstability as analysis substance at room temperature.

Example 5 Electrochemical Stability of [N(C₂H₅)₄][N(CF₃)₂]

In each case, a number of cyclic voltammograms were recordedsuccessively in a measurement cell with platinum electrode, lithiumcounterelectrode and lithium reference electrode. To this end, thepotential was firstly increased, starting from the rest potential, to 6V against Li/Li⁺ at a rate of 20 mV/s and then returned to the restpotential. The electrolyte used was a solution of [N(C₂H₅)₄][N(CF₃)₂] inpropylene carbonate.

The characteristic curve shape shown in FIG. 1 is evident, with anoxidation potential E_(ox) of greater than 5 V against Li/Li⁺.

Example 6 Ionic Conductivity of an Electrolyte Based on[N(C₂H₅)₄][N(CF₃)₂]

With the aid of a 4-pole Knick conductometer, the conductivities of[N(C₂H₅)₄][N(CF₃)₂] in acetonitrile were measured as a function oftemperature and concentration of the conductive salt. In parallel,[N(C₂H₅)₄][BF₄] was measured in acetonitrile. This system represents thecurrent state of the art with respect to “supercapacitor” electrolytesand thus serves as reference. FIGS. 2 and 3 show the results obtained.They confirm that the novel system based on [N(C₂H₅)₄][N(CF₃)₂] hassignificantly improved conductivities.

1. A process for the preparation of a bis(trifluoromethyl)imido salt ofthe general formula (I)M^(a+)[(N(CF₃)₂)⁻]_(a)  (I) wherein M^(a+) is a monovalent or divalentcation, and a=1 or 2, comprising reacting at least onetrifluoromethanesulfonate of the general formula (II)[M^(a+)][(OSO₂CF₃)⁻]_(a)  (II) wherein M^(a+) is a monovalent ordivalent cation, and a=1 or2, with bis(trifluoromethyl)imidorubidium insolution, and the resultant bis(trifluoromethyl)imido salt of thegeneral formula (I) is, if desired, purified and/or isolated.
 2. Aprocess according to claim 1, wherein M^(a+) is a sodium, potassium,cesium, copper or silver cation, and a=1.
 3. A process according toclaim 1, wherein M^(a+) is a mercury, copper, zinc or cadmium cation,and a=2.
 4. A process according to claim 1, wherein a=1 and M^(a+) is acation of the general formula (III)[(R_(b) ¹R_(c) ²R_(d) ³R_(e) ⁴]A_(x))_(y)Kt]⁺  (III) wherein Kt=N, P,As, Sb, S or Se, A=N, P, P(O), O, S, S(O), SO₂As, As(O), Sb or Sb(O),R¹, R², R³ and R⁴ are identical or different and are H, halogen,substituted and/or unsubstituted alkyl C_(n)H_(2n+1), substituted and/orunsubstituted C₁₋₁₈-alkenyl having one or more double bonds, substitutedand/or unsubstituted C₁₋₁₈-alkynyl having one or more triple bonds,substituted and/or unsubstituted cycloalkyl C_(m)H_(2m−1),monosubstituted, polysubstituted and/or unsubstituted phenyl,substituted and/or unsubstituted heteroaryl; where n=1-18, m=3-7, x=0 or1, y=1-4, y=1 for x=0, where b, c, d and e are each=0 or 1, whereb+c+d+e≠0, A may be included in various positions in R¹, R², R³ and/orR4, Kt may be included in a cyclic or heterocyclic ring, and the groupsbonded to Kt may be identical or different.
 5. A process according toclaim 1, wherein the conversion to a bis(trifluoromethyl)imido salt ofthe general formula (I) is carried out at a temperature of −60-+60° C.6. A process according to claim 1, wherein the conversion to abis(trifluoromethyl)imido salt of the general formula (I) is carried outin an organic solvent.
 7. A process according to claim 6, wherein thesolvent used is acetonitrile, benzonitrile, dimethoxyethane and/orpropionitrile or a mixture of acetonitrile, benzonitrile,dimethoxyethane and/or propionitrile.
 8. A process according to claim 1,wherein the solvent comprises ≦0.1% by weight of water.
 9. A processaccording to claim 1, wherein the trifluoromethanesulfonate salt of thegeneral formula (II) or the bis(trifluoromethyl)imidorubidium isemployed in a molar excess of ≦3% or in equimolar amounts.
 10. A processaccording to claim 1, wherein the bis(trifluoromethyl)imido salt of thegeneral formula (I) is purified by filtration after removal of thesolvent.
 11. A process according to claim 1, wherein thebis(trifluoromethyl)imido salt of the general formula (I) is purified byextraction with dichloromethane and/or hexane and/or diethyl ether. 12.A compound of the general formula (I)M^(a+)[(N(CF₃)₂)⁻]_(a)  (I) wherein M^(a+)=Cd²⁺, Zn²⁺ or Cu⁺.
 13. Anelectrolyte comprising at least one salt of the general formula (I)prepared according to claim
 1. 14. An electrochemical cell comprising anelectrolyte according to claim
 13. 15. A process according to claim 1,wherein the conversion is carried out at a temperature of −50-+50° C.16. A process according to claim 1, wherein the conversion is carriedout at a temperature of −45-+30° C.
 17. A process according to claim 1,wherein the conversion is carried out in a polar solvent.
 18. A processaccording to claim 1, wherein the solvent comprises ≦0.01% by weight ofwater.
 19. A process according to claim 1, wherein the solvent comprises≦0.005% by weight of water.
 20. A process according to claim 1, whereinthe bis(trifluoromethyl)imido salt of the general formula (I) ispurified by filtration at a temperature of −90-+30° C.
 21. A processaccording to claim 1, wherein the bis(trifluoromethyl)imido salt of thegeneral formula (I) is purified by filtration at a temperature of−70-+20° C.